Surface potential of hydrogen adsorbed on nickel films and its dependence on film structure

Abstract

Surface potential changes which take place when hydrogen is adsorbed on nickel films have been measured using the static capacitor technique. By variation of the temperature of deposition of the film, and of the temperature of subsequent adsorption of hydrogen, three different adsorbed species have been identified: a negative adatom β^– ₁, a positive pseudo-hydride species β⁺ ₂ and a positive molecularly adsorbed species α. Conditions favourable to the formation of the β⁺ ₂ species are discussed. Surface potential measurements for hydrogen adsorption on Pd and Nb (which easily form hydrides) and on Fe (which does not form a hydride) are consistent with the pseudo-hydride character of the β⁺ ₂ species.